That's fair, I value OEM less for your described reasoning -- if they're worth more then for sure eBay!
I have wondered why sometimes OEM are much more and sometimes they are much less or the same lol
There are 3 main reasons for this:
1. They cost more. Example: Dell buys drives from Seagate. They test them; if the batch has more than a 5% error rate, they return them. They then modify the firmware based on blueprints provided by the manufacturer. They test them again with their hardware. They MAY make modifications restricting some features, but usually only make modifications that allow better compatibility with their hardware (you get a health bar and direct SMART values in iDrac management). They then certify the drives as Dell drives. All of this is expensive and now any responsibility for faults are fully owned by Dell and not Seagate. Thus the cost will always be higher than a Seagate original.
2. A buyer will want to be 100% sure that the hardware they buy is validated for their use case. If you buy a Dell server with non-dell parts, the server is no longer vaiidated by Dell and will usually affect warranty. Usually: you still get 24/7 support for the drives but you will not get on-prem replacement if they find out you are using non certified hardware. There are tricks and tips on getting around this and Dell is usually quite good in helping: they won't replace the non-Dell SSD but they may replace the faulty Dell raid controller. However, technically, using non certified hardware violates the purchase agreement and voids the support you paid for.
3. People selling OEM servers can get more from a brand new system by replacing parts. This is partially unethical if the buyer is not told, but companies sell base models from the OEM's and upgrade the parts bought from 3rd party vendors. Ebay being one of them. If the end-user is unaware that the new server was not from Dell they would be paying a large sum for a fully specc'ed system. A base model may cost $2,000 with 1 CPU and 1 stick of ram, 480GB SSD. The seller replaces and adds another CPU, adds ram and replaces the SSD with 8 x 1.6TB SSD's and is able to sell the server for $15K. This is quite common which is why HPE puts holograms on all their hardware - and chips into their 2.5" caddies. When an OEM sells a 1.92TB SSD for $1K each and a stick of 32GB ram for $400, you better bet they know what's going on. Is the RAM any different from regular Samsung ram? Nope. They may call it smart memory and make the server display an error, but RAM is RAM. As is an SSD. It is very rare that a manufacturer's hardware will present issues that were not caused by the OEM. Rare, but this does not mean it doesn't happen. HPE and Dell know that this rare instance is not worth affecting their reputation, hence they spend a lot on validating everything that they sell with their products.
